Existing wireless system architectural configurations impose stringent constraints on the system designer with regards to receiving communication signals. Moreover, such configurations often provide low reliability communication links, high operating costs, and an undesirably low level of integration with other system components.
As shown in FIG. 1, an exemplary conventional radio frequency (RF) receiver 100 includes an analog radio receiver 105, at least one analog to digital converter (ADC) 110, a controller 115 and a modem 120. The analog radio receiver 105 is a direct conversion receiver which includes an antenna 125 for receiving a wireless communication signal, a bandpass filter 130, a low noise amplifier (LNA) 135, an optional second filter 140 (e.g., bandpass filter), at least one demodulator 145 forming real and imaginary signal paths 150, 155, respectively, a phase-locked loop (PLL) 160 and first and second analog low pass filters (LPFs) 165, 170, for controlling bandwidth selectivity. Alternatively, the analog radio receiver 105 may be a heterodyne receiver.
The modem 120 controls the switching of the LNA 135. The PLL 160 generates a local oscillator (LO) signal to control the real and imaginary signal paths 150, 155, formed by the demodulator 145. The real signal path 150 is an in-phase (I) signal path formed by the demodulator 145 for routing a real signal component of the wireless communication signal. The imaginary signal path 155 is a quadrature (Q) signal path formed by the demodulator 145 for routing an imaginary signal component of the wireless communication signal.
In the exemplary conventional RF receiver 100 of FIG. 1, the ADC 110 is connected to the real and imaginary signal paths 150, 155, via the analog LPFs 165, 170, respectively. An analog real signal component 175 is output from the LPF 165 to a real input port of the ADC 110 and an analog imaginary signal component 180 is output from LPF 170 to an imaginary input port of the ADC 110. Additional components, such as amplifiers and high pass filters (HPFs), may also be optionally coupled between the LPFs 165, 170, and the ADC 110. The ADC 110 outputs digital real and imaginary signal outputs 185, 190. The controller 115 maintains control over all of the active components of analog radio receiver 105 and the ADC 110.
In the analog radio receiver 105, the real and imaginary signal paths 150, 155, and the respective components to which they are coupled, are susceptible to cross-talk interference due to their capacitor-like structure. Thus, significant fringes detrimental to performance of the analog radio receiver 105 may occur between the real and imaginary signal paths 150, 155, including the components coupled thereto, due to their close proximity to one another. Cross-talk interference is the result of energy from the imaginary signal component being induced into the real signal path 150, and/or energy from the real signal component being induced into the imaginary signal path 155, which may cause coupling between the signal paths 150 and 155.
Because the costs of components that process RF analog signals are higher than the components that use DSP, it is desired to provide a digital baseband (DBB) system, including a low cost receiver with low noise and minimal power requirements, which utilizes DSP techniques to compensate for cross-talk interference which occurs between the real and imaginary signal components.